In the 1630s, Bernini began a tempestuous affair with Costanza Bonarelli, the wife of an assistant. Around 1636-38, working for the Borghese family, he portrayed her in a tender, lifelike rendering now in the collection of the Bargello Museum in Florence.
But their idyll was ruined when Bernini caught his brother Luigi sneaking away from her quarters and exploded with rage. The artist sent his servant to her with orders to slash her face. Thus when Bernini carved "Medusa," he viewed her as the mythical creature, a Gorgon, who had been caught having an affair with Neptune. Medusa is being punished—with her hair transformed into writhing snakes and crying out with anguish.
When I pointed out the story to Peter D'Epiro, he quickly shared an image of Costanza Bonarelli made before the provocation (this copy is from this interesting blog):
Here is the more famous After: